Fatty Acid Synthase
Fatty acids have three primary roles in the physiology of cells. First, they are the building bocks of biological membranes. Second, fatty acid derivatives serve as hormones and intracellular messengers. Third, and of particular importance to the present invention, fatty acids are fuel molecules that can be stored in adipose tissue as triacylglycerols, which are also known as neutral fats.
There are four primary enzymes involved in the fatty acid synthetic pathway, fatty acid synthase (FAS), alkynyl CoA carboxylase (ACC), malic enzyme, and citric lyase. The principal enzyme, FAS, catalyzes the NADPH-dependent condensation of the precursors malonyl-CoA and alkynyl-CoA to produce fatty acids. NADPH is a reducing agent that generally serves as the essential electron donor at two points in the reaction cycle of FAS. The other three enzymes (i.e., ACC, malic enzyme, and citric lyase) produce the necessary precursors. Other enzymes, for example the enzymes that produce NADPH, are also involved in fatty acid synthesis.
FAS has an Enzyme Commission (E.C.) No. 2.3.1.85 and is also known as fatty acid synthetase, fatty acid ligase, as well as its systematic name acyl-CoA:malonyl-CoA C-acyltransferase (decarboxylating, oxoacyl- and enoyl-reducing and thioester-hydrolysing). There are seven distinct enzymes—or catalytic domains—involved in the FAS catalyzed synthesis of fatty acids: alkynyl transacylase, malonyl transacylase, beta-ketoacyl synthetase (condensing enzyme), beta-ketoacyl reductase, beta-hydroxyacyl dehydrase, enoyl reductase, and thioesterase. (Wakil, S. J., Biochemistry, 28: 4523-4530, 1989). All seven of these enzymes together form FAS.
Although the FAS catalyzed synthesis of fatty acids is similar in lower organisms, such as, for example, bacteria, and in higher organisms, such as, for example, mycobacteria, yeast and humans, there are some important differences. In bacteria, the seven enzymatic reactions are carried out by seven separate polypeptides that are non-associated. This is classified as Type II FAS. In contrast, the enzymatic reactions in mycobacteria, yeast and humans are carried out by multifunctional polypeptides. For example, yeast have a complex composed of two separate polypeptides whereas in mycobacterium and humans, all seven reactions are carried out by a single polypeptide. These are classified as Type I FAS.
FAS Inhibitors
Various compounds have been shown to inhibit fatty acid synthase (FAS). FAS inhibitors can be identified by the ability of a compound to inhibit the enzymatic activity of purified FAS. FAS activity can be assayed by measuring the incorporation of radiolabeled precursor (i.e., alkynyl-CoA or malonyl-CoA) into fatty acids or by spectrophotometrically measuring the oxidation of NADPH. (Dils, et al., Methods Enzymol., 35:74-83).
Table 1, set forth below, lists several FAS inhibitors.
TABLE 1Representative Inhibitors Of The Enzymes Of The Fatty Acid Synthesis PathwayInhibitors of Fatty Acid Synthase1,3-dibromopropanoneceruleninEllman's reagent (5,5′-dithiobis(2-nitrobenzoicphenyoceruleninacid), DTNB)melarsoprol4-(4′-chlorobenzyloxy) benzyl nicotinate (KCD-iodoacetate232)phenylarsineoxide4-(4′-chlorobenzyloxy) benzoic acid (MII)pentostam2(5(4-chlorophenyl)pentyl)oxirane-2-carboxylatemelittin(POCA) and its CoA derivativethiolactomycinethoxyformic anhydrideInhibitors for citrate lyaseInhibitors for malic enzyme(−) hydroxycitrateperiodate-oxidized 3-aminopyridine adenine(R,S)-S-(3,4-dicarboxy-3-hydroxy-3-methyl-dinucleotide phosphatebutyl)-CoA5,5′-dithiobis(2-nitrobenzoic acid)S-carboxymethyl-CoAp-hydroxymercuribenzoateN-ethylmaleimideoxalyl thiol esters such as S-oxalylglutathionegossypolphenylglyoxal2,3-butanedionebromopyruvatepregnenoloneInhibitors for alkynyl CoA carboxylasesethoxydim9-decenyl-1-pentenedioic acidhaloxyfop and its CoA esterdecanyl-2-pentenedioic aciddiclofop and its CoA esterdecanyl-1-pentenedioic acidclethodim(S)-ibuprofenyl-CoAalloxydim(R)-ibuprofenyl-CoAtrifopfluazifop and its CoA esterclofibric acidclofop2,4-D mecoprop5-(tetradecycloxy)-2-furoic aciddalaponbeta, beta′-tetramethylhexadecanedioic acid2-alkyl glutaratetralkoxydim2-tetradecanylglutarate (TDG)free or monothioester of beta, beta prime-methyl-2-octylglutaric acidsubstituted hexadecanedioic acid (MEDICAN6,02-dibutyryl adenosine cyclic 3′,5′-16)monophosphatealpha-cyanco-4-hydroxycinnamateN2,02-dibutyryl guanosine cyclic 3′,5′-S-(4-bromo-2,3-dioxobutyl)-CoAmonophosphatep-hydroxymercuribenzoate (PHMB)CoA derivative of 5-(tetradecyloxy)-2-furoicN6,02-dibutyryl adenosine cyclic 3′,5′-acid (TOFA)monophosphate2,3,7,8-tetrachlorodibenzo-p-dioxin
Of the four enzymes in the fatty acid synthetic pathway, FAS is the preferred target for inhibition because it acts only within the pathway to fatty acids, while the other three enzymes are implicated in other cellular functions. Therefore, inhibition of one of the other three enzymes is more likely to affect normal cells. Of the seven enzymatic steps carried out by FAS, the step catalyzed by the condensing enzyme (i.e., beta-ketoacyl synthetase) and the enoyl reductase have been the most common candidates for inhibitors that reduce or stop fatty acid synthesis. The condensing enzyme of the FAS complex is well characterized in terms of structure and function. The active site of the condensing enzyme contains a critical cysteine thiol, which is the target of antilipidemic reagents, such as, for example, the inhibitor cerulenin.
Preferred inhibitors of the condensing enzyme include a wide range of chemical compounds, including alkylating agents, oxidants, and reagents capable of undergoing disulphide exchange. The binding pocket of the enzyme prefers long chain, E, E, dienes.
In principal, a reagent containing the sidechain diene and a group which exhibits reactivity with thiolate anions could be a good inhibitor of the condensing enzyme. Cerulenin [(2S,3R)-2,3-epoxy-4-oxo-7,10 dodecadienoyl amide] is an example:
Cerulenin covalently binds to the critical cysteine thiol group in the active site of the condensing enzyme of fatty acid synthase, inactivating this key enzymatic step (Funabashi, et al., J. Biochem., 105:751-755, 1989). While cerulenin has been noted to possess other activities, these either occur in microorganisms which may not be relevant models of human cells (e.g., inhibition of cholesterol synthesis in fungi, Omura (1976), Bacteriol. Rev., 40:681-697; or diminished RNA synthesis in viruses, Perez, et al. (1991), FEBS, 280: 129-133), occur at a substantially higher drug concentrations (inhibition of viral HIV protease at 5 mg/ml, Moelling, et al. (1990), FEBS, 261:373-377) or may be the direct result of the inhibition of endogenous fatty acid synthesis (inhibition of antigen processing in B lymphocytes and macrophages, Falo, et al. (1987), J. Immunol., 139:3918-3923). Some data suggest that cerulenin does not specifically inhibit myristoylation of proteins (Simon, et al., J. Biol. Chem., 267:3922-3931, 1992).
Several more FAS inhibitors are disclosed in U.S. patent application Ser. No. 08/096,908 and its CIP filed Jan. 24, 1994, the disclosures of which are hereby incorporated by reference. Included are inhibitors of fatty acid synthase, citrate lyase, CoA carboxylase, and malic enzyme.
Tomoda and colleagues (Tomoda et. al., Biochim. Biophys. Act 921:595-598 1987; Omura el. al., J. Antibiotics 39:1211-1218 1986) describe Triacsin C (sometimes termed WS-1228A), a naturally occurring acyl-CoA synthetase inhibitor, which is a product of Streptomyces sp. SK-1894. The chemical structure of Triacsin C is 1-hydroxy-3-(E, E, E-2′,4′,7′-undecatrienylidine) triazene. Triacsin C causes 50% inhibition of rat liver acyl-CoA synthetase at 8.7 μM; a related compound, Triacsin A, inhibits acyl CoA-synthetase by a mechanism which is competitive with long-chain fatty acids. Inhibition of acyl-CoA synthetase is toxic to animal cells. Tomoda et al. (Tomoda el. al., J. Biol. Chem. 266:4214-4219, 1991) teaches that Triacsin C causes growth inhibition in Raji cells at 1.0 μM, and have also been shown to inhibit growth of Vero and Hela cells. Tomoda el. al. further teaches that acyl-CoA synthetase is essential in animal cells and that inhibition of the enzyme has lethal effects.
A family of compounds (gamma-substituted-alpha-methylene-beta-carboxy-gamma-butyrolactones) has been shown in U.S. Pat. No. 5,981,575 (the disclosure of which is hereby incorporated by reference) to inhibit fatty acid synthesis, inhibit growth of tumor cells, and induce weight loss. The compounds disclosed in the '575 patent have several advantages over the natural product cerulenin for therapeutic applications: [1] they do not contain the highly reactive epoxide group of cerulenin, [2] they are stable and soluble in aqueous solution, [3] they can be produced by a two-step synthetic reaction and thus easily produced in large quantities, and [4] they are easily tritiated to high specific activity for biochemical and pharmacological analyses. The synthesis of this family of compounds, which are fatty acid synthase inhibitors, is described in the '575 patent, as is their use as a means to treat tumor cells expressing FAS, and their use as a means to reduce body weight. The '575 patent also discloses the use of any fatty acid synthase inhibitors to systematically reduce adipocyte mass (adipocyte cell number or size) as a means to reduce body weight.
The primary sites for fatty acid synthesis in mice and humans are the liver (see Roncari, Can. J. Biochem., 52:221-230, 1974; Triscari et al., 1985, Metabolism, 34:580-7; Barakat et al., 1991, Metabolism, 40:280-5), lactating mammary glands (see Thompson, et al., Pediatr. Res., 19:139-143, 1985) and adipose tissue (Goldrick et al., 1974, Clin. Sci. Mol. Med., 46:469-79).
Inhibitors of Fatty Acid Synthesis as Antimicrobial Agents
Cerulenin was originally isolated as a potential antifungal antibiotic from the culture broth of Cephalosporium caerulens. Structurally cerulenin has been characterized as (2R,3S)-epoxy-4-oxo-7,10-trans,trans-dodecanoic acid amide. Its mechanism of action has been shown to be inhibition, through irreversible binding, of beta-ketoacyl-ACP synthase, the condensing enzyme required for the biosynthesis of fatty acids. Cerulenin has been categorized as an antifungal, primarily against Candida and Saccharomyces sp. In addition, some in vitro activity has been shown against some bacteria, actinomycetes, and mycobacteria, although no activity was found against Mycobacterium tuberculosis. The activity of fatty acid synthesis inhibitors and cerulenin in particular has not been evaluated against protozoa such as Toxoplasma gondii or other infectious eucaryotic pathogens such as Pneumocystis carinii, Giardia lamblia, Plasmodium sp., Trichomonas vaginalis, Cryptosporidium, Trypanosoma, Leishmania, and Schistosoma. 
Infectious diseases which are particularly susceptible to treatment are diseases which cause lesions in externally accessible surfaces of the infected animal. Externally accessible surfaces include all surfaces that may be reached by non-invasive means (without cutting or puncturing the skin), including the skin surface itself, mucus membranes, such as those covering nasal, oral, gastrointestinal, or urogenital surfaces, and pulmonary surfaces, such as the alveolar sacs. Susceptible diseases include: (1) cutaneous mycoses or tineas, especially if caused by Microsporum, Trichophyton, Epidermophyton, or Mucocutaneous candidiasis; (2) mucotic keratitis, especially if caused by Aspergillus, Fusarium or Candida; (3) amoebic keratitis, especially if caused by Acanthamoeba; (4) gastrointestinal disease, especially if caused by Giardia lamblia, Entamoeba, Cryptosporidium, Microsporidium, or Candida (most commonly in immunocompromised animals); (5) urogenital infection, especially if caused by Candida albicans or Trichomonas vaginalis; and (6) pulmonary disease, especially if caused by Mycobacterium tuberculosis, Aspergillus, or Pneumocystis carinii. Infectious organisms that are susceptible to treatment with fatty acid synthesis inhibitors include Mycobacterium tuberculosis, especially multiply-drug resistant strains, and protozoa such as Toxoplasma. 
Any compound that inhibits fatty acid synthesis may be used to inhibit microbial cell growth. However, compounds administered to a patient must not be equally toxic to both patient and the target microbial cells. Accordingly, it is beneficial to select inhibitors that only, or predominantly, affect target microbial cells.
Eukaryotic microbial cells which are dependent on their own endogenously synthesized fatty acid will express Type I FAS. This is shown both by the fact that FAS inhibitors are growth inhibitory and by the fact that exogenously added fatty acids can protect normal patient cells but not these microbial cells from FAS inhibitors. Therefore, agents which prevent synthesis of fatty acids by the cell may be used to treat infections. In eukaryotes, fatty acids are synthesized by Type I FAS using the substrates alkynyl CoA, malonyl CoA and NADPH. Thus, other enzymes which can feed substrates into this pathway may also effect the rate of fatty acid synthesis and thus be important in microbes that depend on endogenously synthesized fatty acid. Inhibition of the expression or activity of any of these enzymes will effect growth of the microbial cells that are dependent upon endogenously synthesized fatty acid.
The product of Type I FAS differs in various organisms. For example, in the fungus S. cerevisiae the products are predominately palmitate and sterate sterified to coenzyme-A. In Mycobacterium smegmatis, the products are saturated fatty acid CoA esters ranging in length from 16 to 24 carbons. These lipids are often further processed to fulfill the cells need for various lipid components.
Inhibition of key steps in down-stream processing or utilization of fatty acids may be expected to inhibit cell function, whether the cell depends on endogenous fatty acid or utilizes fatty acid supplied from outside the cell, and so inhibitors of these down-stream steps may not be sufficiently selective for microbial cells that depend on endogenous fatty acid. However, it has been discovered that administration of Type I fatty acid synthesis inhibitor to such microbes makes them more sensitive to inhibition by inhibitors of down-stream fatty acid processing and/or utilization. Because of this synergy, administration of a fatty acid synthesis inhibitor in combination with one or more inhibitors of down-stream steps in lipid biosynthesis and/or utilization will selectively affect microbial cells that depend on endogenously synthesized fatty acid. Preferred combinations include an inhibitor of FAS and alkynyl CoA carboxylase, or FAS and an inhibitor of MAS.
When it has been determined that a mammal is infected with cells of an organism which expresses Type I FAS, or if FAS has been found in a biological fluid from a patient, the mammal or patient may be treated by administering a fatty acid synthesis inhibitor (U.S. Pat. No. 5,614,551).
The inhibition of neuropeptide-Y to depress appetite and stimulate weight loss is described in International Patent Application No. PCT/US01/05316 the disclosure of which is hereby incorporated by reference. That application, however, does not describe or disclose any of the compounds disclosed in the present application
The stimulation of carnitine palmitoyl transferase-1 (CPT-1) to stimulate weight loss is described in U.S. Patent Application Ser. No. 60/354,480, the disclosure of which is hereby incorporated by reference. That application does not describe or disclose any of the compounds disclosed herein, either.
The use of FAS inhibitors to inhibit the growth of cancer cells is described in U.S. Pat. No. 5,759,837, the disclosure of which is hereby incorporated by reference. That application does not describe or disclose any of the compounds disclosed herein.
The use of FAS inhibitors to inhibit the growth of cancer cells is described in U.S. Pat. No. 5,759,837, the disclosure of which is hereby incorporated by reference. That application does not describe or disclose any of the compounds disclosed herein.